Adjustable magnetic trip means for circuit breakers with single adjustment means



I April 7, 1970v I E. GRYCTKO 3,505,623l

I ADJUSTABLE MAGNETIC. TRIP MEANS FOR CIRCUT BREAKERS WITH SINGLE ADJUSTMENT MEANS Filed Aug. 9, 1968 2 sheets-sheet 1 ECE-1.5.

April 7, 1970 N c. E. GRYCT'KO 3,505,623 ADJUSTABLE MAGNETIC TRIP. MEANS vFOR CIRCUIT BREAKERS WITH SINGLE ADJUSTMENT MEANS Filed Aug. 9, 1968 2 Sheets-Sheet 2 ff-EEZ.

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l 5 l Mia/www ,yf 4'/ i .if ff l 47 l IZ l fa 40N 4 /f i /f l A| 4.7 f2 I N l Z@ Z/ 2 n ,y ff i l" 1N VEA/TORA aff/fz 5. .gm/crea United States Patent O U.S. Cl. 335--42 9 Claims ABSTRACT OF THE DISCLOSURE A magnetic trip structure for circuit vbreakers in which the range of operation is extended andthe point of operation isadjustably selected by manipulation of a single control device. A stationary magnet which cooperates with a movable armature is provided with a variable air gap which can be adjusted to adjust the reluctance of the magnetic circuit. This, in turn, adjusts the point at which the armature is attracted to the magnet in order to trip a circuit breaker. A single'v adjustment means is connected to the movable reluctance adjustment structure by a cam mechanism. This common adjustment structure may be further connected toladjust the armature air gap, whereby a common cam initially causes a major adjustment of the magnetic circuit reluctance and thereafter causes a change in the armature air gap, thereby to have an extended adjustment range for the trip point of the system.

This invention relates to magnetic trip .structures for circuit breakers, and more particularly relates to a novel magnetic trip structure which has a single adjustment means available externally of the circuit breaker for adjusting the point within an extended adjustment range at which the circuit breaker will be tripped by a fault current.

Circuit breakers are commonly provided with magnetic trip devices which cause instantaneous tripping of the circuit breaker responsive to a fault current which exceeds a particular magnitude. Such devices commonly consist of a stationary magnet structure which receives a conductor which carries the current passing through the circuit breaker contacts. A movable armature is then provided for the magnet structure and is attracted to the magnet structure against the force of a biasing spring when the current through the conductor extending through the magnet structure reaches a sufficiently high value to generate la ux sufficiently strong to attract the armature against the force of the biasing spring.

It willv be apparent that the current value at which the armature is attracted to the-magnet (and thereby effects tripping of the circuit breaker trip mechanism in the usual manner) depends upon the armature air gap with respect to the stationary magnet structure and the strength of the biasing spring.

Either or both the air gapkand biasing spring force have been made adjustable in the past in order to adjust the point at which the armature will be attracted to the magnet, thereby to adjust the instantaneous trip point of the circuit breaker. This is most commonly accomplished by adjusting the armature air gap.

In this type arrangement, however, the adjustment of the armature air gap alone causes an inherent restriction on the range of adjustment which `is permissible, since the adjustment of the armature air gap inherently alters the biasing force of the spring associated with the armature. Therefore, an attempt, for example, to increase the current at which instantaneous tripping will occur could be accomplished by increasing the armature air gap. This,

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however, has the effect of decreasing the spring biasing force attempting to hold the armature open, thereby partially offsetting the increased instantaneous current requirements set by the increased armature air gap. Ar similar action occurs where the air gap is decreasedin order to require a lower instantaneous current for operation of the circuit breaker trip mechanism, since the biasing force tending to hold the armature open will be increased. Therefore, the counteraction of the changing air gap by the changing spring force has the effect of limiting the possible range of adjustment in the aforementioned type of system.

These eiiects could, of course, be partially overcome by providing a separate adjustment structure for both the air gap and the spring biasing force. This, however, requires the manipulation of two individual adjustments in a properly coordinated manner which is sometimes extremely diicult to achieve in the eld by relatively untrained personnel.

Another method for adjusting the instantaneous current value required to trip the circuit breaker has been through the control of the reluctance of the magnetic circuit. This type arrangement is shown, for example, in the patent to Hobson, 2,939,929, wherein the stationary magnet is provided with a control air gap. Thus, by varying the control air gap, it is possible to adjust the instantaneous current required to generate a particular force in order to close the armature of the magnet structure.

This type arrangement, however, has always been used in combination with a separately adjustable armature air gap and separately adpustable biasing spring, whereby one having to adjust the instantaneous trip characteristics of a circuit breaker using the mechanism of the abovenoted patent will have to manipulate three separate adjustments in a properly coordinated manner. As pointed out above, this would be exceptionally dicult, especially where the adjustment is made in the eld by relatively untrained personnel.

The principle of the present invention is to incorporate a novel magnetic reluctance control means in a magnetic trip device which can be operated from a single control adjustment which is available externally of the circuit breaker. In a preferred embodiment of the invention, a magnetic trip device is provided with a variable reluctance portion in the stationary magnet structure, and is further provided with means for adjusting the armature air gap. A single adjustable member is then provided which initially acts to adjust the magnetic reluctance .of the circuit and thereafter acts to adjust the armature air gap. The combination of these two adjustments which are made through a common operating member therefore permits a considerable extension of the range of instantaneous adjustment which was not possible in the prior art type systems using an adjustable armature air gap, and further permits the adjustment to be made by unskilled personnel, since only a single adjustment member is manipulated with the adjuster being unaware of the mechanism by which the adjustment is obtained. That is to say, the adjustment of reluctance and then armature air gap occurs in an automatic sequential process which does not require the exercise of judgment by the user of the apparatus other than the manipulation of the single control means.

Accordingly, a primary object of this invention is to provide a novel magnetic trip structure having an increased adjustment range.

Another object of this invention is to provide a novel magnetic trip structure incorporating magnetic reluctance control with a single externally available operating means to be manipulated by the user.

A further object of this invention is to provide a novel instantaneous trip structure for circuit breakers which has a single adjustment member and an extended range of adjustment.

These and other objects of this invention will become apparent from the following description taken in connection with the drawings in which:

FIGURE 1 illustrates the condition which is obtained when one attempts to adjust the instantaneous trip by adjustment of armature air gap only.

FIGURE 2 is a perspective diagram of a first embodiment of the present invention.

FIGURE 3 is a cross-sectional view of the embodiment of FIGURE 2.

Referring iirst to FIGURE 1, there is illustrated the conditions which exist when one attempts to adjust armature air gaps in a typical prior art system in which a biasing spring is used to bias the armature to a disengaged position with respect to the magnet. Thus, in a given adjustment position, the force on the armature, as current increases, is shown by the solid line curve 10. The spring force is shown as solid straight line 11. Once the magnetic force attracting the armature exceeds the biasing force of the spring, the armature will be attracted against the force of its biasing spring so that the armature will move into the magnet and thereby operate the circuit breaker trip mechanism.

In order to increase the current at which the armature will close, the armature air gap may be increased so that the rise in armature force as a function of the current can be depicted by the dotted line 12. An increase in the air gap, however, will necessarily cause a decrease in the biasing force of the spring to the force F2 depicted by dotted line 13. Therefore, the trip system will now operate at the current l2.

In a similar manner, if the system is to trip at a lower current, the air gap for the armature can be decreased to the dot-dash. line 14 which will cause a necessary increase in the spring biasing force to the dot-dash line 15 for force F3 so that the breaker will now operate at the current I3.

The consequent change in spring biasing force with an adjustment of the armature air gap can be seen from FIGURE 1 to impose a necessary limitation on the maximum range of adjustment available in the magnetic trip system. That is to say, where the air gap is increased so that armature force follows dotted line 12, the designer might wish to have the range extended to the point at which dotted line 12 causes the solid line force characteristic 11. This point, however, is not available to the designer because of the decrease in the force characteristics of the spring to dotted line 13.

In a similar manner, the lower current range is restricted because of the increase in spring biasing force, as shown by line 15.

In accordance with the present invention, a novel tripping structure is provided in which the magnetic reluctance of the magnetic circuit is varied to alter the trip point for the circuit breaker, thereby permitting an extremely wide range of adjustment of the trip point since a fixed armature position and xed biasing force for the armature biasing spring may be retained.

This change in magnetic reluctance which is achieved by a single operating member may be further ganged to a second armature air gap adjustment operation in a predetermined sequence and from a common operating member. The permissible range of adjustment, however, is not limited as described in FIGURE 1, in view of the added range obtained from the initial reluctance adjustment.

FIGURES 2 and 3 illustrate the invention in schematic fashion for the case of an instantaneous magnetic trip structure for any typical circuit breaker which may opcircuit breaker 20 which is connected in series between terminals 21 and 22 through a main load conductor 23. Circuit breaker 20 may be of any standard variety which includes a magnetic trip means and will have an automatic trip mechanism 24 which is operated from a tripper bar 2S which may be of a standard type. The magnetic trip system then includes a stationary magnetic core 26 which receives conductor 23. 'Ihe magnetic circuit of stationary magnet 26 is completed by a movable magnetic structure 27 and a stationary magnetic structure 28 which is spaced from movable structure 27 by a xed air gap 29. A magnetic armature 30 then completes the magnetic path for the magnetic structure through the air gaps 31 and 32. Note thatstructures 26, V27 and 28 may be formed of stacked laminations formed as shown in FIG- URE 2, although any desired magnet structure could be used.

Armature 30 is secured to a stem 33 which is suitably guided for axial movement by guide means (not shown), and is biased upwardly by means of compression spring 34 which tends to hold the armature 30 in an open position. Stem 33 then` extends through a suitable opening in trip lever 25, and is terminated by a head 35 which, when armature 30 is attracted downwardly and toward stationary magnet 26, will engage trip lever 25 to operate trip mechanism 24.

In accordance with the invention, the trip characteristics of the system are adjusted by movement of the suitably guided magnetic member 27 in the direction of the arrows, thereby to open or close air gap 36 which adjusts the reluctance of the magnetic circuit including armature 30 so as to require a higher or smaller current in conductor 23 in order to attract armature 30 and trip the trip mechanism 24. Note that the gap 29 remains fixed during this adjustment process and that the gaps 31 and 32 remain relatively fixed over at least a rst and major portion of the adjustment of the air gap 36.

The adjustment mechanism includes a rotatable cam 40 having an upper cam surface 41 and lower cam surface 42. Upper cam surface 41 consists of a relatively long, low platform section 43 and a remaining step-shaped section of increasing height. An inwardly bent stern 44 is then secured tov magnetic member 27, and extends through spring retaining structure 45 which carries a compression spring 46 for holding the inwardly bent portion 47 of stern 44 against the upper face of cam 40. Cam 40 is then suitablyy rotatably secured in any desired manner as by the use of snap-rings 48Y and 49 which hold cam stem 50 on opposite sides of the circuit breaker outer housing 51. It will be apparent that as the adjustment stem 50 is rotated, stern 44 will be raised or lowered, depending upon which portion of upper cam surface 40 is engaged by inwardly turned stem portion 47. This, in turn, will adjust the position of magnet portion 27 and air gap 36.

In accordance with an important feature of the invention, and after a minimum reluctance has been obtained through a minimum setting for air gap 36, the lower portion 42 of cam 40 begins to adjust air gaps 31 and 32. That is to say, armature 30v is provided with an auxiliary cam follower stem 55 which engages the lower portion 42 of cam 40. The cam surface 42 is relatively flat in the region at which it engages stern follower 55 and while inwardly bent stem 47 engages cam surface 41. However, once follower 47 reaches the at cam surface portion 43, the curvature of cam 42 increases downwardly at 42a so that continued rotation in the same direction of cam 40 after the minimum air gap 36 is reached will cause the beginning of a substantial decrease in the armature air gaps 31 and 32. This adjustment will then proceed in the prior art manner for the adjustment of armature air gap, where, however, the adjustment range of the system has been increased because of the initial adjustment of the magnetic reluctance of the magnetic circuit. Note further that the entire adjustment is made through a single rotatable member (cam 40 and stem 50) so that the operator need not know which portion of the structure is being adjusted.

Although this invention has been described with respect to particular embodiments, it should be understood that many variations and modifications will now be obvious to those skilled in the art, and, therefore, the scope of this invention is limited not by the speciic disclosure herein, but only by the appended claims.

The embodiments of the invention in which an exclusive privilege or property is claimed are deined as follows:

1. A magnetic trip system comprising a stationary magnet structure, an electrical conductor extending through said stationary magnet structure and generating a magnetomotive force around said stationary magnet structure; an armature movable with respect to said stationary magnet structure and magnetically attracted toward said stationary magnet by a force related to the current through said electrical conductor; biasing means connected to said armature biasing said armature away from said magnet; and adjustable reluctance means connected to said stationary magnet structure for adjusting the magnetic reluctance of said stationary magnet structure; and single control means connected to said adjustable reluctance means comprising the sole means for adjusting the current value at which said armature is moved toward said stationary magnet structure against the force of said biasing means.

2. The system of claim 1 wherein said adjustable reluctance means includes a movable magnetic structure forming an adjustable air gap in said stationary magnet structure.

3. The system of claim 2 which further includes air gap adjustment means for adjusting the maximum spacing of said armature from said stationary magnet structure; said single control means further connected to said air gap adjustment means; said control means having a rst and a second movement range; movement of said control means through said iirst movement range moving said movable magnet structure; movement of said control means through said second movement range moving said air gap adjustment means.

4. In combination; a circuit breaker having a trip mechanism and a magnetic trip system; said magnetic trip system comprising a stationary magnet structure, an electrical conductor extending through said stationary magnet structure and generating a magnetomotive force around said stationary magnet structure; an armature movable with respect to said stationary magnet structure and magnetically attracted toward said stationary magnet by a force related to the current through said electrical conductor; biasing means connected to said armature biasing said armature away from said magnet; and adjustable reluctance means connected to said stationary magnet structure for adjusting the magnetic reluctance of said stationary magnet structure; and -single control means connected to said adjustable reluctance means comprising the sole means for adjusting the current value at which said armature is moved toward said stationary magnet structure against the force of said biasing means; said armature connected to said trip mechanism and tripping said trip mechanism responsive to movement of said armature to said stationary magnet structure.

5. The combination of claim 4 wherein said circuit breaker has an enclosure; said single control means extending through said enclosure and being accessible external of said circuit breaker.

6. The combination of claim 5 wherein said adjustable reluctance means includes a movable magnetic structure forming an adjustable air gap in said stationary magnet structure.

7. The combination of claim 6 which further includes air gap adjustment means for adjusting the maximum spacing of said armature from said stationary magnet structure; said single control means further connected to said air gap adjustment means; said control means having a first-and a second movement range; movement of said control means through said first movement range moving said movable magnet structure; movement of said control means through said second movement range moving said air gap adjustment means.

8. A magnetic trip system comprising a stationary magnet structure, an electrical conductor extending through said stationary magnet structure and generating a magnetomotive force around said stationary magnet structure; an armature movable with respect to said stationary magnet structure and magnetically attracted toward said stationary magnet by a force related to the current through said electrical conductor; biasing means connected to said armature biasing said armature away from said magnet; and adjustable reluctance means connected to said stationary magnet structure for adjusting the magnetic reluctance of said stationary magnet structure; and single control means connected to said adjustable reluctance means comprising the sole means for adjusting the current value at which said armature is moved toward said stationary magnet structure against the force of said biasing means; said sole control means comprising a rotatable structure having a cam surface connected to said adjustable reluctance means.

9. The system of claim 8 wherein said adjustable reluctance means includes a movable magnetic structure forming an adjustable air gap in said stationary magnet structure which further includes air gap adjustment means for adjusting the maximum spacing of said armature from said stationary magnet structure; said single control means further connected to said air gap adjustment means; said control means having a first and a second movement range; movement of said control means through said irst movement range moving said movable magnet structure; movement of said control means through said second movement range moving said air gap adjustment means; said rotatable structure having a second cam surface connected to said air gap adjustment means.

References Cited UNITED STATES PATENTS 2,915,683 12/1959 Lewis 335--273 X 3,188,427 6/1965 Cooper et al 335-204 BERNARD A. GILHEANY, Primary Examiner R. N. ENVALL, JR., Assistant Examiner U.S. C1. X.R. 335-176, 198 

